Tips for abstract screening in a systematic review.
The search is over
Four stages of abstract screening
Let’s consider each stage in detail.
1. Plan
In this way, reviewers can then go straight to the next report without needing to complete the remaining questions. A trained librarian or information specialist will be able to advise you on screening questions and provide expert guidance based on experience.Once agreed, the team can document the review’s eligibility criteria in the Review Settings section in Covidence for display above the abstracts for easy reference during screening.
At the planning stage you will also allocate the task of screening to two or more members of your team. Using two or more reviewers, who must work independently, provides a check on decisions and reduces the risk that a study is included or excluded incorrectly. Conflicting decisions (one reviewer wants to include a study, another wants to exclude it) take time to resolve. Effort invested in the planning phase – for example on a thorough team briefing – will repay you in efficiencies down the line. We will return to the issue of conflict resolution during stages two, three, and four.
2. Pilot
3. Screen
Congratulations, your search for studies is complete. You have followed the process specified in your protocol and reached an important milestone in your systematic review. You now have hundreds, or perhaps thousands, of references and a review team eager to take a closer look. So what’s next?
The number of references you retrieve from a search can be daunting. In the process of manually selecting some of these studies for further investigation your team will make important decisions and any of these can introduce bias. Good study selection requires a rigorous process and the first stage in that process is abstract screening.
At the abstract screening stage you will keep the references that meet the inclusion criteria for your review and those that you are unsure about. You will dismiss the rest. The references you keep will move to the next stage in the selection process: full-text screening.
Abstract screening presents an opportunity to save time in the study selection process because reports correctly excluded here will reduce the amount of full-text screening needed later. It is worth taking the time to plan abstract screening carefully and to think about it in the context of the flow of information through your review, from the identification of references, through the screening and eligibility checks, to the eventual exclusion or inclusion of studies in the analysis (see figure 2)¹. These guidelines will help you to develop and implement an abstract screening process that is straightforward and reliable.
It’s useful to consider four key stages of abstract screening:
Before the screening begins it’s important to organise and store the references efficiently; for example, in a reference management software, or Covidence. Your choice of tool will depend on factors such as the type of systematic review and the number of references. These guidelines are for systematic reviews that have identified 1000 or more references.
Preparing to screen involves formulating questions based on the review’s prespecified eligibility criteria. The questions should be as simple and unequivocal as possible. It’s a good idea to sort questions in order of importance so that a reference can be excluded as soon as it fails to meet a criterion, for example:
It’s impossible to foresee all the potential complications that your team could encounter during screening. Pilot-testing a small set of references (Cochrane recommends six to eight including a definite yes, a definite no, and a maybe) will uncover some of them. Perhaps an ambiguous question or a gap in communication has caused a reviewer to reach an incorrect decision on the eligibility of some studies. This creates a conflict that needs to be investigated. Issues like this one can be identified and effectively addressed after the pilot-test and before the screening is scaled up to the whole reference set.
Before beginning large-scale screening, review teams may carry out automated deduplication processes available in reference management software, and Covidence automatically deduplicates all references imported into review projects.
Reviewers may also identify duplicate references during the screening process; these are two or more identical references that might be the result of searching multiple databases. Review teams can agree a process for managing these as part of the planning process.